This application pertains to the art of electrical equipment and, more particularly, to potential spark generating electrical equipment such as circuit breakers, switches, motor starters, and the like for use in hazardous environments.
The invention finds specific application in housing and actuating electrical equipment in explosive or potentially explosive environments, that is, in environments where the air may contain fumes or dust which could be ignited by a spark. The present invention is also advantageous in other hazardous environments, e.g., environments in which the air has a high moisture content, underwater applications, and the like.
Heretofore, various mechanisms have been proposed for actuating switches, circuit breakers, and the like in hazardous environments. These prior art devices commonly comport with the requirements of various international and national safety codes. Most commonly, potentially sparking or arcing electrical equipment is placed in a housing or enclosure through which mechanical mechanisms extend for actuating the equipment from the exterior of the housing. An electrical receptacle is commonly connected with the housing for selectively receiving an electrical plug from controlled electrical machinery. Although sealed to a large extent, the housing is rarely completely sealed to the highly pervasive ignitable gases and dusts. Rather, the housing is designed to prevent an internal ignition from passing to the atmosphere. This is commonly accomplished by designing the housing as a pressure vessel capable of withstanding pressures up to 1,000 psi and otherwise preventing the housing from rupturing if an internal ignition should occur. Further, the various ports and apertures through the housing for accommodating mechanical actuating mechanisms, electrical conductors, and the like are designed to form thin flame paths which are elongated sufficiently to cool any flame or hot particles before exiting at the atmospheric end of the path.
Various mechanisms have been used to prevent a spark during removal of the plug from the housing receptacle. Some devices have provided a direct mechanical linkage within the housing extending from the receptacle to the switch in such a manner that insertion of the plug turns the switch "on" and removal of the plug turns the switch "off". Others have provided mechanical interlocks between an external switch operating handle and the receptacle which prevent the plug from being removed unless the switch is in its "off" position. Still others have provided a mechanical locking mechanism extending between the receptacle and the mechanical actuating mechanism. Such locking mechanisms prevented the switch from being moved to its "on" position unless a plug was received in the receptacle and/or prevented plug removal from the receptacle unless the switch was in its "off" position. Devices of this general type are shown, for example, in U.S. Pat. No. 1,818,290 issued August 1931 to W. A. Wulle and U.S. Pat. No. 2,015,543 issued September, 1935 to C. H. Bissell.
Various problems have been observed in the prior art actuation mechanisms. In those mechanisms in which the interaction between the plug and receptacle move the enclosed switch between its "on" and "off" positions, a spark may be caused between the plug and receptacle. Those actuating mechanisms which allow the switch to be operated in the absence of a plug fully mated in the receptacle are unsuitable for applications in which the switch is connected with a source of power.
In view of the foregoing, it has been considered desirable to develop a new and improved actuating mechanism. The subject development contemplates such an arrangement which overcomes the above-referenced problems and others.